1. Field of the Disclosure
The present disclosure relates to a capacitive humidity sensor, and more particularly, to a capacitive humidity sensor and a manufacturing method thereof capable of increasing reliability of the sensor by forming a dehumidification layer of a polymer material having a large surface area between a lower electrode layer and an upper electrode layer while miniaturizing the humidity sensor by forming a sensor unit on an ROIC substrate.
2. Discussion of the Background Art
Generally, a capacitive humidity sensor is manufactured so that a polymer layer for dehumidification is formed between electrodes at both ends thereof and a change in a charge amount induced to both ends of the electrode depends on a change in dielectric constant by the dehumidification of the polymer layer and a change in an induced charge accordingly.
The capacitive humidity sensor has more complicated manufacturing process and is more expensive than a resistive humidity sensor that uses a change in resistance according to a change in humidity due to voltage applied to both ends thereof to measure humidity. However, for the reason of high stability and reliability in characteristics, the capacitive humidity sensor has been mainly used for expensive measurement.
FIG. 1 shows a perspective view of a structure of a capacitive humidity sensor according to the related art.
An insulating layer 120 of SiO2, Si3N4, SiOxNy, or the like is formed on a silicon substrate 110. Further, a sensor unit 160 and a readout integrated circuit (ROIC) 170 are formed on the silicon substrate on which the insulating film 120 is formed.
In reviewing a method of manufacturing the sensor unit 160, a lower electrode layer 130 is formed on the insulating layer 120 by depositing and patterning a metal layer such as aluminum (Al) and platinum (Pt). Then, a dehumidification layer 140 is formed on the lower electrode layer 130 by spin coating and patterning a polyimide (PI) layer and is subjected to heat treatment at a temperature between 200° C. to 300° C.
An upper electrode layer 150 in a comb shape is formed on the polyimide dehumidification layer 140 by depositing and patterning the metal layer of the same material as the lower electrode layer 130, thereby manufacturing the capacitive humidity sensor having a parallel plate capacitor structure in which the polyimide dehumidification layer 140 is formed between the upper electrode layer 150 and the lower electrode layer 130.
In this case, the reason of forming the upper electrode layer 150 in a comb shape differently from the lower electrode layer 130 is to smoothly pass water molecule into the polyimide dehumidification layer 140. That is, this is to partially expose the polyimide dehumidification layer 140.
After the sensor unit 160 is formed as described above, the ROIC 170 is formed on the silicon substrate in which the sensor unit 160 is not present. Since an electrical phenomenon such as current, voltage, or the like, that are generated by the ROIC 170 may affect the humidity sensor, it is preferable that the ROIC 170 is formed to be maintained at a predetermined distance from the sensor unit 160.
However, the capacitive humidity sensor according to the related art has a limitation in miniaturization of the humidity sensor since the sensor unit and the ROIC unit are horizontally positioned on a single substrate.
Further, the characteristics of the capacitive humidity sensor, such as sensitivity, are determined by unique characteristics of the polymer. Since the capacitive humidity sensor according to the related art has a sandwich structure in which the dehumidification layer of the polymer is inserted between both electrodes, thereby making it difficult to improve the sensitivity of the dehumidification layer.
The present disclosure has been made in an effort to provide a capacitive humidity sensor and a manufacturing method thereof capable of increasing reliability of the sensor by forming a dehumidification layer of a polymer material having a large surface area between a lower electrode layer and an upper electrode layer while miniaturizing the humidity sensor by forming a sensor unit on an ROIC substrate.